Phenolic membranes with tunable sub-10-nm pores for nanofiltration and tight-ultrafiltration

Membranes with sub-10-nm pores are receiving growing interest in recognizing and separating nanocolloids, biomolecules, and soluble salts from water, but suffer from difficulty of optimizing pore structures and inferior stability. Herein, we report an efficient method for the preparation of robust nanoporous phenolic membranes with widely tunable pore sizes in the range of nanofiltration and tight-ultrafiltration. Solutions of resol precursors and poly(ethylene glycol)s (PEGs) are spin-coated to form thin films and then heated to thermopolymerize resols into phenolics. Subsequently, the films are treated in H₂SO₄ solution to degrade PEGs, producing nanoporous phenolic membranes. Thus-prepared phenolic membranes exhibit adjustable effective pore sizes and tunable separation performances from nanofiltration to tight-ultrafiltration, which is otherwise inaccessible. Due to the thin thicknesses and rich water channels, the membranes exhibit higher permeances than other tight-ultrafiltration membranes and commercial ultrafiltration membranes with similar rejections. Furthermore, thanks to the robust frameworks and good chemical resistance of phenolics, the membranes deliver stable performances in long-term operations, elevated pressures, and acidic conditions. This work provides a facile and universal strategy for the synthesis of membranes with sub-10-nm pores for nanofiltration and tight-ultrafiltration.